fix(models): synchronize canonical runtime selection

tests/bus/test_runtime_events.py

@@ -10,6 +10,7 @@ from nanobot.bus.runtime_events import (
     SessionTurnStarted,
     TurnCompleted,
     TurnRunStatusChanged,
+    TurnRuntimeAdmitted,
 )
 
 
@@ -123,6 +124,37 @@ async def test_runtime_event_publisher_consumes_turn_metadata_on_complete() -> N
     assert second.runtime is None
 
 
+@pytest.mark.asyncio
+async def test_runtime_event_publisher_exposes_admitted_runtime() -> None:
+    bus = RuntimeEventBus()
+    seen: list[object] = []
+    publisher = RuntimeEventPublisher(bus)
+    msg = InboundMessage(
+        channel="websocket",
+        sender_id="user",
+        chat_id="chat-a",
+        content="hello",
+    )
+    runtime = object()
+    bus.subscribe(seen.append)
+
+    await publisher.turn_runtime_admitted(msg, "websocket:chat-a", runtime)  # type: ignore[arg-type]
+    await publisher.turn_completed(
+        channel="websocket",
+        chat_id="chat-a",
+        session_key="websocket:chat-a",
+        metadata=None,
+    )
+
+    admitted = seen[0]
+    completed = seen[1]
+    assert isinstance(admitted, TurnRuntimeAdmitted)
+    assert admitted.runtime is runtime
+    assert admitted.context.chat_id == "chat-a"
+    assert isinstance(completed, TurnCompleted)
+    assert completed.runtime is runtime
+
+
 @pytest.mark.asyncio
 async def test_runtime_event_publisher_emits_persisted_turn_attributes() -> None:
     bus = RuntimeEventBus()